We have isolated myocytes from adult canine hearts for preparation of subcellular fractions highly enriched in lysosomes and sarcolemma. The very pure sarcolemma is enriched up to 75 to 90-fold (over homogenate levels) in ouabain - inhibited (Na ion plus K ion)-Mg2 ion-ATPase and specific beta-receptor binding. Moderately pure lysosomes (25- to 30-fold) have phospholipase A, active at acid pH, which is inhibited dramatically by chlorpromazine; lysophosphatidyl choline is decreased significantly by this drug. Both of these organelles are under study to determine the specific mechanisms by which ischemia and acidosis perturb their integrity and impair enzymes and structural lipids associated with each organelle.